The present invention relates to methods and compositions for treating subterranean formations, and more specifically, to foamed treatment fluids, foaming additives, and associated methods.
Treatment fluids have been utilized in the treating of subterranean formations, e.g., for stimulation or sand control treatments such as fracturing or gravel packing, respectively. In fracturing treatments, a treatment fluid is pumped through a well bore into a subterranean formation at a rate and pressure such that one or more fractures are created or enhanced in a portion of the formation. The treatment fluid may comprise particulates, often referred to as “proppant particulates,” that are deposited in the fractures. The proppant particulates function to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. Treatment fluids used in fracturing treatments may comprise, in addition to water, a gelling agent to increase the viscosity of the fluid and stabilize the foamed fluid, enabling it to carry more and/or larger proppant. In order to reduce the subsequent flowback of proppant particulates and other particulates with the produced fluids, the last portion of the proppant particulates introduced into the fractures has heretofore been coated with an adhesive substance. As used herein, the term “adhesive substance” refers to a material that is capable of being coated onto a particulate and that exhibits a sticky or tacky character which, when applied to proppant that is slurried in a treatment fluid, causes the proppant particulates having adhesive substance thereon to have a tendency to create clusters or aggregates due to the effect of the closer pressure and temperature. As used herein, the term “tacky,” in all its forms, generally refers to a substance having a nature such that it is (or may be activated to become) somewhat sticky to the touch. Typically, the proppant particulates coated with the adhesive substance may be deposited in the fracture after a large quantity of uncoated proppant particulates have been deposited therein.
Treatment fluids are also utilized in completion operations such as gravel packing. In gravel pack treatments, the treatment fluid suspends gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation zones, to form a gravel pack to enhance sand control. One common type of gravel packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size designed to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the particulates from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the treatment fluid is often reduced to allow it to be recovered. The gravel particulates may be coated with an adhesive substance, inter alia, to help prevent formation fines and sand from invading the gravel pack and thereby reducing the production potential of the well. In some situations, fracturing and gravel packing treatments are combined into a single treatment to provide stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place, and the fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the fracturing treatment usually ends in a screen-out condition, creating an annular gravel pack between the screen and casing. This allows both the fracturing treatment and gravel pack to be placed in a single operation.
In carrying out subterranean treatment operations, the treatment fluids often may be foamed, wherein the treatment fluid further comprises a surfactant and a gas. In addition to being lightweight, foamed treatment fluids may effectively carry particulates (e.g., proppant particulates, gravel particulates, etc.) and also may require a smaller amount of gelling agent, reducing the amount of residue left in the subterranean formation by the gelling agent. Additionally, foamed treatment fluids have low fluid loss properties, reducing or removing the need for a fluid loss control additive. Foamed treatment fluids generally include one or more additives that facilitate the formation of and stabilize the foam, especially at higher temperatures where the foam tends to break down. However, many of these additives may react with and destroy the adhesive substance that may be coated on the particulates within the foamed treatment fluid, inhibiting particulate deposit and thus decreasing potential hydrocarbon production.